Evaluating residual stress profile in cold drawn 1018 steel rods using finite element analysis

This work explores a finite element (FE) method based residual stress profile estimation technique for cold drawn steel rods. The surface contour method is a well-known technique in which displacement normal to the lateral cut is used in the FE model to estimate residual stress. However, the lateral cut can affect residual stress, leading to error in estimation. In this work, the samples were cut axially at different locations throughout thickness and the warp on the sample were measured and matched using FE analysis. Two categories of samples were prepared from the same rectangular cold drawn steel bar by milling. (I) samples with only top surface cut of different depth and (ii) samples with EDM cut at different positions through thickness.

The finite element analysis has two steps: the 1^st step is to generate residual stress, and the 2^nd step is to match the deflections after the cut. A 2D model was developed using uncut sample dimensions. Nodal displacements were applied to generate stress profile. Longitudinal nodal stresses were transferred to the 2^nd model. Element death was applied to eliminate the cut portion of the sample. The resultant deflection was analyzed and the residual profile in the 1^st step was changed accordingly. Several stress distribution profiles were developed until a best matched residual stress was found.

The results that best matched between finite element and experiment showed a residual stress profile of tension-compression-tension. The residual stress profile was further modified to no stress in the middle region to match the EDM cuts deflections. This shows that the profile can be estimated using the approach presented here. The advantage of this approach is that the deflection over the length can be used for optimization, which will allow us to get unique solutions to the stress profile.